Tool and method for layer depalletizing

ABSTRACT

The problem of potentially damaging a pallet layer that is gripped by clamps of a depalletizing tool is solved i) by detecting the real position of the layer using a pad on the tool that is movable with the clamps towards the pallet layer and whose detected stopping position determines the real position of the layer, and ii) while the layer is gripped by the clamp, by inserting under the layer curtains; the pressure on the layer by the clamps being adapted to the ease to go underneath the layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/001,676, filed on May 22, 2014, the contents of which areincorporated by reference herein.

FIELD

The present disclosure relates to depalletizing, and more specificallyto a tool for layer depalletizing.

BACKGROUND

Distribution centers usually receive full pallets of goods frommanufacturers. Those goods are stored in a warehouse section and areretrieved and palletized according to the retailers' needs.Traditionally, the products were depalettized manually from the fullpallets in the inbound area. This task is physically demanding and anautomated approach is required for productivity and health & safetyreasons.

U.S. Pat. No. 8,915,696 B2 issued on Dec. 23, 2014 to Baumann et al. andbeing titled “Device and Method for Depalletizing Stacked Bundles”describes a robotized system and method where stacked containers aredepalettized.

The depalletizing tool from Baumann possesses a base frame 1 and twounderside support base parts 2 a and 2 b that can be moved towards andaway from one another by means of slide bearings 3 a, 3 b. Each supportbase part includes a roller as a leading edge.

A drawback of the tool from Baumann is that the rollers tend to wearwith time, are costly to replace and they have a minimal diameter thatcan cause a problem when small products have to be picked. Also, thisapproach relies solely on the friction action of the rollers to insertthe movable support member underneath the products. Therefore, if thetool is not precisely positioned at the right height, the rollers coulddamage the products as they try to lift them with their rotating action.

Also, the tool by Baumann includes light barriers as sensors to positionthe tool for the depalletizing process. This approach does work wellwhen the products to be depalettized have a regular shape, do not haveany open flap, and when all products are nicely stacked. If thoseconditions are not respected, the use of light barriers can cause falsereadings yielding a misguiding of the depalletizing device.

Also, the method and tool by Baumann cannot handle the slip sheets thatare often inserted between the layers for their separation.

U.S. Pat. No. 7,934,759 B2, issued on May 3, 2011 to Weller and beingtitled “Packaging System Including Pallet De-Layering System” describesa system and method to handle a layer of multiple palletized productswhere an interior void is located in the product layer. The systemincludes void filling members carried by a gripper mechanism that isprovided to improve holding the products for de-layering.

The approach taken by Weller only works if there is at least one void inthe layer of products, which is too restrictive.

SUMMARY

The problem of potentially damaging a pallet layer that is gripped byclamps of a depalletizing tool is solved i) by detecting the realposition of the layer using a pad that is movable with the clampstowards the pallet layer and whose detected stopping position determinesthe real position of the layer, and ii) while the layer is gripped bythe clamp, when inserted under the layer curtains; the pressure on thelayer by the clamps being adapted according to the front end ease to gounderneath the products.

According to an illustrative embodiment, there is provided a tool forlayer depalletizing comprising:

-   -   a frame for mounting the tool to a robot;    -   clamps movably mounted to the frame to grip a pallet layer;    -   curtains mounted to the frame below the clamps and being movable        under the pallet layer while the pallet layer is gripped by the        clamps; pressure on the clamps being adjusted depending on a        movement resistance of the curtains when the curtains are        inserted under the pallet layer.

According to another illustrative embodiment, there is provided a toolfor layer depalletizing comprising:

-   -   a frame for mounting the tool to a robot;    -   clamps movably mounted to the frame to grip a pallet layer; and    -   a pad, mounted to the frame above the clamps, that is        transversely movable towards and away a level defined by the        clamps, and that defines a reference to determine a height of        the pallet layer when the pad is moved towards the pallet layer.

According to still another illustrative embodiment, there is provided acurtain assembly mounted to a layer depalletizing tool under clampsthereof comprising:

-   -   two curtains, each defined by a plurality of rolls mounted in        tracks so as to be slidably movable under a pallet layer while        the pallet layer is gripped by the clamps; each of the plurality        of rolls extending transversally to directions of movement of        the curtains; each of the two curtains including a front end        equipped with at least one rotatable friction element.

According to another illustrative embodiment, there is provided a methodfor layer depalletizing comprising:

-   -   positioning clamps around at least one layer to depalletize;    -   using the clamps to grip and at least partially lift the at        least one layer;    -   moving curtains under the at least one layer while monitoring a        displacement speed thereof;    -   if the displacement of the curtains is indicative of a product        blocking the movement of the curtains, then applying less        pressure on the clamps;    -   moving the layer with the clamps to a selected area, while the        curtains are maintained under the at least one layer; and    -   at the selected area, removing the curtains from under the at        least one layer and the clamps releasing the at least one layer.

According to a further illustrative embodiment, there is provided amethod for layer depalletizing comprising:

-   -   determining a real position of a layer by moving a pad towards a        top surface of the layer;    -   positioning clamps around the layer using the real position of        the layer;    -   using the clamps to grip and at least partially lift the layer;    -   moving curtains under the layer;    -   moving the layer with the clamps to a first area, while the        curtains are maintained under the layer; and    -   at the first area, removing the curtains from under the layer        and the clamps releasing the layer.

Illustrative embodiments of the layer depalletizing tool includepressure adjustment of its side clamps to facilitate the gripping of theproducts located at the center of the layer (i.e. inside those locatedat the perimeter).

In a layer depalletizing tool according to illustrative embodiments, thetop pad allows measuring the height of the top surface of the layer tobe picked for precise positioning of the tool. Such a top pad alsoprevents small products to “pop out” as curtains move underneath theproducts or when the curtains are opened when the products are placed.

Other objects, advantages and features of the tool and method fordepalletizing mixed load products will become more apparent upon readingthe following non restrictive description of preferred embodimentsthereof, given by way of example only with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a top perspective of a tool for layer depalletizing accordingto a first illustrative embodiment; the tool being shown attached to arobot arm;

FIG. 2 is a top perspective of the tool from FIG. 1;

FIG. 3 is a top plan view of the tool from FIG. 1;

FIG. 4 is an exploded perspective of the tool from FIG. 1, the toolbeing shown without most of its frame;

FIG. 5 is a top perspective of part of the frame and of the curtainactuating assembly;

FIGS. 6A and 6B are respectively top and bottom perspective view of thetool from FIG. 1, shown in position to grip a full pallet layer;

FIGS. 7A and 7B are perspective views similar to FIGS. 6A and 6Brespectively, showing the clamps applying pressure on the pallet layerand the curtains being partially closed;

FIGS. 8A and 8B are perspective views similar to FIGS. 6A and 6Brespectively, showing the clamps having released some of the pressure onthe pallet layer and the curtains being completely closed;

FIG. 9 is a flowchart of a method for layer depalletizing according to afirst illustrative embodiment; and

FIG. 10 is a perspective of a clamp assembly according to a secondillustrative embodiment.

DETAILED DESCRIPTION

In the following description, similar features in the drawings have beengiven similar reference numerals, and in order not to weigh down thefigures, some elements are not referred to in some figures if they werealready identified in a precedent figure.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one”, butit is also consistent with the meaning of “one or more”, “at least one”,and “one or more than one”. Similarly, the word “another” may mean atleast a second or more.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “include” and “includes”) or “containing”(and any form of containing, such as “contain” and “contains”), areinclusive or open-ended and do not exclude additional, unrecitedelements.

A tool 10 for layer depalletizing according to a first illustrativeembodiment will now be described with reference to FIGS. 1 to 5.

As shown in FIG. 1, the tool 10 according to the first illustrativeembodiment is operatively mounted to an industrial robot arm 12, whichis conventionally coupled to a robot controller 14.

The expression “controller” should be construed broadly as including oneor more electronic devices, including for example one or more computersthat are configured with components and/or programmed with instructionsthat produce one or more functionalities, including controlling both arobot and a tool attached to the robot.

The robot 12 is in the form a standard industrial articulated robot armsuitable for the application. A conventional robot arm can be used, suchas ABB's or IRB 760, FANUC's M410, or any similar robot arm offered byother manufacturers like Kuka or Motoman for example.

In the description and in the claim, the expressions ‘robot’ and ‘robotarm’ will be used interchangeably to mean a programmable systemincluding articulated and/or movable members that can receive, controland move a tool.

Since the operation of a robot and of a robot controller is believed tobe well known in the art, it will not be described herein in more detailfor concision purposes.

As an input, a pallet (not shown), made of one or more layers 16 ofproducts 18 (see FIG. 6B for example), is positioned in front of therobot 12. Slip sheets (not shown) can be present between the layers 16of products 18. They can be removed with other means or left on theremoved layer. The output includes one layer 16 removed from the palletand placed for example on an outfeed conveyor (not shown).

In some embodiments, the slip sheet positioned above the layer ofproducts is removed at the same time. In this case, the layer 16 isplaced for example on an outfeed conveyor and the slip sheet is droppedin a bin (not shown).

Each layer 16 is made from a plurality of similar products 18 and eachpallet is made of a plurality of layers 16. The products 18 can besimilar or different from one layer 16 to the other. Also, the layers 16can be full or partial, i.e. products can cover the complete surface ofthe layer 16 or some free space or openings can be found on the surfaceof the layer 16.

The expression “product” should be construed herein as including anytype of case, carton, tray, shrink wrapped bundle or tray, etc.Generally, the product is of a rectangular shape. They can containbottles, cans, pouches, bags, etc.

The product dimensions may vary greatly between each different type ofproduct 18. For example, their height can be between 2″ and 24″.

The layer depalletizing tool 10 comprises a frame 20, four side clamps22-24 movably mounted to the frame 20 to grip and release a pallet layer16, two curtains 26 mounted to the frame under the clamps 22-24 to beinserted under a pallet layer 16 gripped by the clamps 22-24, and a toppad 28, mounted to the frame 20 above the clamps 22-24.

The frame 20 comprises two pairs of parallel walls 30-32 assembled so asto generally define a rectangular perimeter. Each wall 30 and 32includes a bottom rectangular portion 34 and 36 respectively and anintegral triangular portion 38 and 40 respectively. The two triangularportions 40 are slightly bent toward each other.

The frame 20 further comprises two transversal rectangular hollow tubes42 and 44, extending respectively parallel to the walls 30 between thewalls 32, and parallel to the walls 32 between the walls 30. Holes 45(see FIG. 6A) are provided near the top of the triangular portions 38-40of the walls 30-32, where the hollow tubes 42 and 44 are secured,allowing passage for connectors and cables (not shown) through the walls30-32 and then through the hollow tubes 42 and 44.

A mounting bracket 46 (see FIG. 6A) is secured to both hollow tubes 42and 44, at the intersection thereof and that allows attaching the tool10 to the robot arm 12.

The frame components 30-44 are assembled using fasteners and/or weldingand so are other parts of the tool 10 that are mounted to the frame 20.

The frame 20 is not limited to the above-described embodiment and othermembers can be provided to mount the tool 10 to the robot arm 12 and tooperatively receive the other components thereof.

As can be better seen in FIG. 4, each facing pair of side clamps 22 and24 are slidably mounted to a respective track 43 and 45, each fixedrespectively underneath hollow tubes 42 and 44 for movement therealongvia mounting assemblies 48 and 50 respectively. Since the mountingassemblies 48 and 50 are very similar, only the mounting of one of theclamp 22 to the frame 20 will be described herein in more detail.

The mounting assembly 48 includes a bracket 52 that is slidably mountedto the hollow tube 42 via the track 43 thereunder, and attached to thedistal ends of rods 60 of the two actuators 56. The bar 54 fixedlyconnects the clamp 22 to the bracket 52. The bar 54 is so mounted to thebracket 52 as to extend perpendicularly therefrom and to the clamp 22.The clamp 22 is perpendicular to the hollow tube 42 in a plane thatincludes the bar 54.

Two pneumatic actuators 56 are provided between the hollow tube 42 andthe bracket 52 to cause movement thereof, and therefore also themovement of the clamp 22 along the hollow tube 42. More specifically,the body 58 of each actuator 56 is secured to the hollow tube 42 onrespective lateral side thereof and the distal end of the rod 60 of theactuator is fixedly mounted to the bracket 52.

The clamps 22 and 24 are moved in parallel pair to grip a pallet layerfrom two opposite sides thereof and then from the other sides. Theactuators 56 are therefore operated four (4) at first (secured on a samehollow tube 42 or 44), and then the other four simultaneously. Accordingto another embodiment, all clamps 22 and 24 are actuated simultaneously.

Providing the nominal dimension of a pallet layer 16, each pair ofclamps 22 and 24 are movable between an extended position to a retractedposition where the clamps 22 or 24 apply a pressure onto the layer 16from corresponding opposite sides.

While the clamps 22 and 24 have different widths, clamps according toanother embodiment may have the same width.

Clamps according to another embodiment (not shown) are pivotally mountedto the frame. According to other embodiment (not shown), the clamps haveother configuration than those illustrated herein, and are mounted tothe frame so as to be differently movable relative to the frame.

With reference to FIGS. 5, 7A and 8B, both curtains 26 are defined by aseries or metallic rolls 62 that are both slidably and rotatably mountedto the rectangular portions 34 of the frame 20 therebetween. Together,both curtains 26 extend along the full length of the portions 34, eachspanning half the length.

More specifically, each roll 62 is provided at its longitudinal endswith hub portions 63 (see FIG. 8B) that are received in parallel tracks64 mounted to the inner face of the frame 10. Each of the four (4)tracks extends along the bottom edge 66 of the rectangular portion 34,from the center thereof to the end of an accurate portion 68 of thetracks 64 that raises towards the triangular portion 38 near thelongitudinal end side of the wall 30. The arcuate portions 68 defines acurtain receiving portion when the curtains 26 are opened.

It is to be noted that, in some Figures, some of the rolls 62 are notshown to alleviate the views.

Each curtain 26 includes at its front end a rotating head 70, which isslidably mounted in the tracks 64 along with the rolls 62 and alsorotatably mounted to the tracks 64.

The rolls 62, along with the head 70 of each curtain 26, are moved alongtheir respective tracks 64 by an actuator 72. The body 74 of theactuator 72 is secured to the rectangular portion 34 of one of the wall30 on the outer face thereof, and its rod 76 is fixedly mounted to thehead 70 via a mounting bracket 78 (FIG. 7B) for translation of the head70 in unison with the rod 76 along the track 79, which is attached tothe outer face of the rectangular portion 34.

When the curtains 26 open, the actuators 72 pushes the heads 70 alongthe tracks 64 forces the rolls 62 in the same direction. When thecurtains 26 close, the actuators 72 pulls the heads 70 along the tracks64 in the same direction.

The heads 70 are in the form of a plurality of rotatable frictionelements 80 extending along the front edge of each curtain 26. Thefriction elements 80 are in the form of rubber O-rings mounted onto twoparallel rolls 82 for rotation thereon in an endless manner. The tworolls 82 are rotatably mounted to the mounting brackets 78 therebetween.

As can be better seen in FIGS. 5 and 7B, the two rolls 82 of eachcurtain 26 are driven by a drive assembly including i) one side chain 84extending along the straight portion of respective tracks 64, and beingmounted to a driving sprocket 86 and a driven sprocket 87, the laterfixed at the end of each roll 82, ii) a drive 90 secured to the wallportion 34 and operatively coupled to one of the two chains 84 via arespective one of the driving sprockets 86. The chains 84 are sopositioned relative to the two rolls 82 via the sprockets 87 so thatrolls 82 and associated chains 84 rotate in unison. Rotation of eachdrive 90 therefore causes the rotation of the O-rings 80. A personskilled in the art will now appreciate that the head 70 can both rotateand slide along the tracks 64 at the same time and independently.

An end roll 92 is provided between the two driven sprockets 88 of eachcurtain 26 to further ease the displacement of the heads 70 along thetracks 64 by linking the chains 85 located at each end of the heads 70therefore assuring that the heads 70 remain perpendicular to the tracks64.

It is to be noted that elements of the drive assembly, including thebelts 84 have been omitted in some drawings to alleviate the views.

With reference more specifically to FIGS. 2-4, the top pad 28 and itsactuating mechanism will now be described.

The top pad 28 is in the form of a plate that is movable towards andaway a pallet layer 16 gripped by the clamps 22-24. The top pad 28 ismade movable by its mounting to the frame 10 via a pad actuatingassembly 100. The plate is made of a soft resilient material, such asrubber or plastic, which is reinforced on its non-contacting face withmetal tubes. According to other embodiments, the pad 28 is made ofanother material and/or is not reinforced.

The pad actuating assembly 100 includes four pad holder shafts 102-108that are rotatably mounted to the frame 20, eight pad holder wheels 110mounted in parallel pairs on each shafts 102-108, four link elements112, each secured to both the top pad 28 and the wheels 110 of arespective shaft 102-108 therebetween, four shaft pulleys 114-120, eachone secured near one end of each shaft 102-108, a top pad linearactuator 122 secured to the frame 20, a pulley assembly 124 fixedlymounted to the frame 20, and four cables 126-132, each one operativelycoupling a respective shaft pulley 114-120 to the movable end of theactuator 122.

The four pad holder shafts 102-108 are rotatably mounted to the hollowtubes 42-44 via four support brackets 134. Together the four shafts102-108 are relatively positioned end to end in a square configuration.

Each link elements 112 is secured to a respective pair of wheels 110 forpartial winding thereon and fixedly to the plate 28 via an attachment136.

The pulley assembly 124 includes a support 138, secured to the hollowtube 42 so as to be positioned at the movable end of the actuator 122,and three (3) intermediary pulleys 140-144 rotatably mounted to thesupport 138 thereunder.

As can be better seen in FIG. 3, the intermediary pulleys 140-144 andthe position and orientation of the actuator allows connecting the fourshaft pulleys 114-120 to the actuator's rod 146 using the cables126-132.

In operation, the top pad 28 is raised by causing the actuator 122 toretract its rod 146, thereby simultaneously pulling onto the cables126-132. This causes the shafts 102-108 to simultaneously rotates,yielding a pulling force onto the link elements 112 that raises the toppad 28. The reverse effect is obtained by extending the actuator rod146.

The operation of the tool 10 will now be described with reference toFIGS. 6A-8B and to FIG. 9, which describes a full layer depalletizingmethod 200 according to an illustrative embodiment.

When the robot controller 14 receives a signal indicative that a palletlayer 16 is ready to be picked (step 202), the controller 14 uses areceived nominal position of the layer to be picked to command the robot12 to position the tool 10 so that the clamps 22 and 24 surround thelayer 16 (step 204) (see FIGS. 6A and 6B).

It is to be noted that, for most layer depalletizing tools, systems andmethods from the prior art, the positioning of the tool relies solely onthe nominal vertical position of the layer.

It is however known in the material handling industry that products 18are often crushed within a pallet by the weight of the layer 16 orlayers located above. This is of course particularly true for the lastlayers sitting directly on the pallet to be depalettized. Therefore, thenominal position of each layer 16, used in the initial programming ofthe robot 12, can lead to a wrong positioning of the tool, limiting thecapacity of the system to adequately depalletize the layers 16.

The top pad 28 is coupled with a sensor (not shown) allowing to evaluatethe real height/position of the top surface 148 of the layer 16 beingpicked, therefore enabling the tool 10 to be positioned more precisely.This added precision enables the depalletizing system, including therobot 12 and tool 10, to be more efficient and reduces the probabilityof product damages or even avoid cases where the bad positioningprevents the products 18 of being depalettized.

The sensor can be in the form of an analog laser distance sensor or anyother similar means.

In step 206, the top pad 28 is lowered and positioned over the top layeron the pallet.

The robot 12 positions the tool 10 to the theoretical height of thelayer 16 to be picked. Knowing that the top pad 28 contacts the uppersurface of the layer 16, the sensor measures its position. Thecontroller 14 then computes the real height of the layer 16 with thetheoretical height and, if necessary, adjusts the tool 10 positionaccordingly.

Using the top pad 28 to determine the real height of the top surface ofthe pallet represents a robust way to achieve this task. For example,even if a flap of a product 18 is lifted or a product 18 is not wellpositioned, the top pad's overall position is not affected and willtherefore provide a valuable and precise information about the realheight of the layer 16. When needed, the robot 12 adjusts the height ofthe tool 10 (step 210).

Considering that each layer 16 can be composed of a plurality ofproducts 18, it often happens that some products 18 have no side facingthe exterior of the layer. According to the first illustrativeembodiment, a combination of mechanisms is provided that allows theclamps to grip them adequately.

First, the four clamps (22-24) are used to compress the whole layer oneach side without horizontally moving the layer (step 212) by activatingand controlling the pneumatic actuators 56.

The robot 12 then slightly lifts the tool 10 to create a gap mainlybetween the lower surfaces 150 of the products 18 located on theperimeter of the layer 16 and the top surface of the products 18 of thelayer 16 just underneath (step 214).

The closing of the horizontal curtains 26 is then initiated so that theyare inserted under the layer 16 (step 216). This step is illustrated inFIGS. 7A and 7B.

The rotating friction heads 70 of the curtains 26 contribute to move theproducts 18 from the gripped layer 16 over the horizontal curtains 26.This more specifically allows the products 18 that are not located onthe perimeter of the layer 16 and that are generally only partiallylifted by the side clamps 22-24 or sometimes not lifted at all to moveover the horizontal curtains 26.

The friction created on the vertical faces of the products 18 by thepressure of the clamps 22-24 sometimes prevents the products 18 to moveupward to enable the horizontal curtains 26 to close underneath withoutdamaging the products 18. When this happens, the pressure isautomatically reduced on the side clamps 22-24 so the above mentionedfriction is also reduced, therefore facilitating the movement of thecurtains 26 to lift and pick the remaining products 18 of the layer 16to be picked.

Variation on the pressure of the clamps 22-24 is adjusted, in step 218,by monitoring the linear movement of the horizontal curtains 26. If aproduct 18 prevents this movement, the horizontal curtains 26 cannotmove forward. When this happens, it is concluded that at least oneproduct 18 is blocking the movement. Therefore, the pressure is reducedon the clamps 22-24 by the actuators 56 (step 220) to continue with theprocess of picking all the products 18 on the layer 16.

According to another embodiment, the linear movement of the curtains 26is monitored so as to detect a movement resistance thereof even when thecurtains continue to move.

When the curtains 26 are completely closed (see FIGS. 8A-8B), the layeris completely gripped by the tool 10 (step 222), and the robot 12 movesthe tool 10 with the gripped layer 16 and transfers the layer 16 to anoutfeed location and the method continues with step 204.

In addition to the above-described function of allowing a preciseassessment of the position of the top layer 16 of the pallet, the toppad 28 also prevents that small products 18 ““pop out” of the layer 16as the horizontal curtains 26 move underneath. Such movement of products18 would occur for example when the layer 16 is composed of smallproducts 18, i.e. products 18 with reduced height. The weight of the toppad 28 is sufficient to prevent the “pop out” effect of small productswithout limiting the capacity of the horizontal curtains 26 to gounderneath them. Similarly, the top pad 28 prevents the small products18 to “pop out” when the horizontal curtains 26 are removed fromunderneath the products 18.

In some applications, slip sheets (not shown) are provided between somelayers 16 of products 18 in a pallet. A standard approach is to have anindependent device that automatically removes the slip sheets betweeneach layer depalletizing sequence. This approach works well but is quiteexpensive considering the addition of the independent device.

According to a further embodiment (not shown), the tool for layerdepalletizing is provided with a component that retrieves a slip sheet(not shown) located over the layer 16 of products 18 at the same timethe layer 16 is depalettized.

Since such a tool is similar to the tool 10, and since this furthermethod is similar to the method 200, for concision purposes, only thedifferences therebetween will be described with reference to FIG. 9.

The tool includes a top pad including suction cups (not shown) to removeany slip sheet over the layer 16 at the same time the layer 16 isdepalettized. When the layer 16 is completely gripped by the tool (step222), the suction cups are activated (step 224). Another laser sensor(not shown), which is facing downward towards the gripped pallet, or thesame referred to hereinabove, is used to determine if there is a slipsheet attached to the top pad 28. As the robot 12 lifts and transfersthe layer 16, the top pad 28 is slightly lifted (step 226). If the lasersensor still detects the presence of an object (step 228), this meansthat there is a slip sheet over the layer 16 being depalettized (step229) and the vacuum is kept on the suction cups (step 230). The robot 12then drops the slip sheet in a bin (236) after the layer 16 is placed onthe outfeed conveyor (step 232) or somewhere else. In the contrary, ifthe sensor does not detect anything, this means that there is no slipsheet over the layer being depalettized. When such is the case, thevacuum is removed from the suction cups and the robot 12 directly movesback to pick the next layer 16 on the pallet once the previous layer 16is placed on the outfeed conveyor (step 238).

Turning now to FIG. 10, a further embodiment of the clamps 322 and 324will now be described briefly. The clamps 322-324 are adapted for atleast two different lengths and at least two different widths of palletlayers 16. According to this embodiment, the lateral side portions ofthe clamps 322 and 324 are provided with respective fingers 326 and 328that allows a first positioning of the clamps 322-324 for smaller palletlayers, wherein the fingers 326 and 328 are completely interlaced, i.e.two adjacent clamps 322 and 324 intersect near the proximate ends oftheir fingers 326 and 328. A second positioning of the clamps 322-324 isfurther allowed for bigger pallet layers (not shown), wherein there isno interlacing between two adjacent clamps 322 and 324. The clamps322-324 can also take intermediary positions wherein there is partialinterlacing between two adjacent clamps 322 and 324.

In such an embodiment of the clamps 322-324, double stroke actuators(not shown) are used instead of the single stroke actuators 56. When asmaller size pallet is depalettized, one stroke action of the doublestroke actuator is kept retracted and only the other stroke action isused to open or closed the clamps. Such a shorter stroke movementreduces the travel of the clamps 322-324, and thus the cycle time.

When a larger size pallet is depalettized, one stroke action of thedouble stroke actuator is kept extended and only the other stroke actionis used to open or closed the clamps.

According to another embodiment, the layer depalletizing tool can gripmore than one layer, depending of the products' height and weight andthe size of the clamps.

It is to be noted that many other modifications could be made to thedepalletizing tools and methods described hereinabove and illustrated inthe appended drawings. For example:

-   -   the robot arm can be replaced by a gantry type equipment or any        other similar means;    -   the layer can be placed on an output conveyor, a pallet, a        table, a platform, an AGV or any other means that can accept the        layer;    -   in some applications, the tool is provided with only one pair of        facing clamps;    -   the shape and length of the clamps may be different than those        illustrated;    -   other friction reducing elements than the rotating heads 70 can        be used in the front end of the horizontal curtains;    -   the mechanism to move the top pad towards and away the gripped        pallet can be different than illustrated and so is the pad;    -   the various actuators to move the top pad, the side clamps and        the curtains can be pneumatic, electric, servo driven or any        other way;    -   other devices than a laser sensor can be used to confirm the        presence of a slip sheet when a layer is being depalettized.

It is to be understood that embodiments of the layer depalletizing toolare not limited in their application to the details of construction andparts illustrated in the accompanying drawings and describedhereinabove. Other embodiments can be foreseen and practiced in variousways. It is also to be understood that the phraseology or terminologyused herein is for the purpose of description and not limitation.

What is claimed is:
 1. A tool for layer depalletizing comprising: aframe for mounting the tool to a robot; clamps movably mounted to theframe to grip a pallet layer; curtains mounted to the frame below theclamps and being movable under the pallet layer while the pallet layeris gripped by the clamps; pressure on the clamps being adjusteddepending on a movement resistance of the curtains when the curtains areinserted under the pallet layer.
 2. The tool as recited in claim 1,having two curtains that are slidably mounted to the frame.
 3. The toolas recited in claim 2, wherein each of the two curtains includes a frontend provided with at least one rotatable friction element.
 4. The toolas recited in claim 3, wherein the at least one rotatable frictionelement includes a series of O-rings mounted in an endless beltarrangement onto two rotatable rollers extending along the width of thecurtain.
 5. The tool as recited in claim 2, wherein each curtainincludes a series of rolls extending transversally to directions ofmovement of the curtains.
 6. The tool as recited in claim 2, wherein thetwo curtains are slidably mounted in tracks secured to the frame.
 7. Thetool as recited in claim 6, wherein each track includes an arcuateportion at one of its ends that receives at least part of the curtainswhen the curtains are opened.
 8. The tool as recited in claim 1, whereinthe curtains are made movable by at least one actuator.
 9. The tool asrecited in claim 1, further comprising a pad, mounted to the frame abovethe clamps, that is transversely movable towards and away a leveldefined by the clamps, and that defines a reference to determine aheight of the pallet layer when the pad is moved towards the palletlayer.
 10. The tool as recited in claim 1, wherein the clamps areslidably mounted to the frame.
 11. The tool as recited in claim 1,wherein the clamps include two pairs of parallel clamps; the clampsbeing slidably mounted to the frame in a rectangular configuration. 12.The tool as recited in claim 11, wherein the clamps are made movable inunison in parallel pair.
 13. The tool as recited in claim 1, whereineach clamp is made movable by at least one actuator.
 14. The tool asrecited in claim 1, wherein the clamps are provided with finger elementsat both lateral sides; the finger elements being configured andpositioned so that finger elements of adjacent clamps can be interlaced.15. A tool for layer depalletizing comprising: a frame for mounting thetool to a robot; clamps movably mounted to the frame to grip a palletlayer; and a pad, mounted to the frame above the clamps, that istransversely movable towards and away a level defined by the clamps, andthat defines a reference to determine a height of the pallet layer whenthe pad is moved towards the pallet layer.
 16. The tool as recited inclaim 15, wherein the pad is movable via a pad actuating assemblyincluding: a plurality of shafts, each rotatably mounted to the frame; aplurality of links attached to the pad at a first end and to arespective shaft at a second other end for partial winding thereon; alinear actuator secured to the frame; a pulley assembly secured to theframe; and a plurality of cables, each one for operatively coupling arespective shaft to the linear actuator via the pulley assembly;whereby, in operation, a translating movement of the linear actuator inone of two linear directions causes the rotation of the plurality ofshafts in a corresponding one of two rotation directions, causing thepad to a corresponding one of raising and lowering.
 17. The tool asrecited in claim 15, wherein the pad includes suction elements to handlea slip sheet.
 18. A curtain assembly mounted to a layer depalletizingtool under clamps thereof comprising: two curtains, each defined by aplurality of rolls mounted in tracks so as to be slidably movable undera pallet layer while the pallet layer is gripped by the clamps; each ofthe plurality of rolls extending transversally to directions of movementof the curtains; each of the two curtains including a front end equippedwith at least one rotatable friction element.
 19. The curtain assemblyas recited in claim 18, wherein sliding of the curtains along the tracksis actuated by at least one first actuator and rotation of the at leastone friction element is actuated by at least one second actuator. 20.The curtain assembly as recited in claim 19, wherein each of the atleast one second actuator is operatively coupled to the at least onerotatable friction element by a coupling assembly including for eachcurtain: a driving element endlessly mounted to the frame along thetracks; a drive mounted to the frame and being operatively coupled tothe driving element for rotation in unison therewith; and the at leastone rotatable friction element that is coupled to the driving elementfor rotation in unison therewith.
 21. The curtain assembly as recited inclaim 18, wherein the at least one rotatable friction element includes aseries of O-rings mounted in an endless belt arrangement onto tworotatable rollers extending along the width of the curtain.
 22. A methodfor layer depalletizing comprising: positioning clamps around at leastone layer to depalletize; using the clamps to grip and at leastpartially lift the at least one layer; moving curtains under the atleast one layer while monitoring a displacement thereof; if thedisplacement of the curtains is indicative of a product blocking themovement of the curtains, then applying less pressure on the clamps;moving the layer with the clamps to a selected area, while the curtainsare maintained under the at least one layer; and at the selected area,removing the curtains from under the at least one layer and the clampsreleasing the at least one layer.
 23. The method as recited in claim 22,further comprising, after positioning the clamps at a nominal positionof the layer around the at least one layer to depalletize: determining areal position of the at least one layer by moving the pad towards a topsurface of the at least one layer; the clamps being positioned aroundthe layer using the real position of the layer.
 24. A method for layerdepalletizing comprising: determining a real position of a layer bymoving a pad towards a top surface of the layer; positioning clampsaround the layer using the real position of the layer; using the clampsto grip and at least partially lift the layer; moving curtains under thelayer; moving the layer with the clamps to a first area, while thecurtains are maintained under the layer; and at the first area, removingthe curtains from under the layer and the clamps releasing the layer.25. The method as recited in claim 24, further comprising verifying apresence of a slip sheet on the layer and if a slip sheet is detected,then dropping the slip sheet at a second area.
 26. The method as recitedin claim 25, wherein verifying a presence of a slip sheet includes:lifting the layer while creating a vacuum thereunder and monitoring adistance of an object under the pad when the layer is lifted; a nonvariation of the distance being indicative of the presence of a slipsheet.
 27. The method as recited in claim 24, wherein said by moving thepad towards a top surface of the layer includes further moving alocation sensor in unison with the pad; the position sensor beingpositioned behind the pad with regards to the layer while both aremoving; the location sensor monitoring its relative position with thepad; the real position of the layer being determined as corresponding toa position of the pad when the relative position of the sensor with thepad changes.